6
cannot assign mismatch length to masked array
pandas
30911
Raise code
# `np.place` on the other hand uses the ``new`` values at it is
# to place in the masked locations of ``values``
np.place(values, mask, new)
# i.e. values[mask] = new
elif mask.shape[-1] == len(new) or len(new) == 1:
np.putmask(values, mask, new)
else:
raise ValueError("cannot assign mismatch length to masked array")
else:
np.putmask(values, mask, new)
def validate_putmask(values: ArrayLike, mask: np.ndarray) -> Tuple[np.ndarray, bool]:
"""
Validate mask and check if this putmask operation is a no-op. """
Links to the raise (1)
https://github.com/pandas-dev/pandas/blob/b3e335254f46a526ee3ce9bb757eac4011d9d1fe/pandas/core/array_algos/putmask.py#L169Ways to fix
1
Steps to reproduce:
Step 1: Create a new directory using the command
$ mkdir test-pandas
Step 2: Navigate to that our new directory using the command
$ cd test-pandas
Step 3: Run the following command
$ pipenv shell
Step 4: To reproduce the exception we need a pre-release version of pandas as the function putmask_without_repeat which can be used to reproduce the exception was introduced in the pre-release version 1.3.0rc1. To install this version of pandas run the following command:
$ pipenv install --pre pandas==1.3.0rc1
Step 5: Run the code:
from pandas.core.array_algos.putmask import putmask_without_repeat
import numpy as np
arr = np.arange(1, 10)
mask = arr > 5
new = arr ** 2
# Remove one element from the new list to make it 9 elements
new = np.delete(new, 0)
# Since, the array and new lsit has mismatched length i.e 10 and 9 resp. thus, exception is caused
putmask_without_repeat(arr, mask, new)
print(arr)
The above code raises the following exception:
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-37-4223aa6afd21> in <module>()
12
13 # Since, the array and new lsit has mismatched length i.e 10 and 9 resp. thus, exception is caused
---> 14 putmask_without_repeat(arr, mask, new)
15 print(arr)
/usr/local/lib/python3.7/dist-packages/pandas/core/array_algos/putmask.py in putmask_without_repeat(values, mask, new)
166 np.putmask(values, mask, new)
167 else:
--> 168 raise ValueError("cannot assign mismatch length to masked array")
169 else:
170 np.putmask(values, mask, new)
ValueError: cannot assign mismatch length to masked array
Fixed version of code:
from pandas.core.array_algos.putmask import putmask_without_repeat
import numpy as np
arr = np.arange(1, 10)
mask = arr > 5
new = arr ** 2
putmask_without_repeat(arr, mask, new)
print(arr)
Explanation:
The pandas putmask_without_repeat function takes three positional arguments namely arr, mask and new. If the new argument specified is a list then, its length should be either 1 or equal to the length of the array supplied. Else, both will have a mismatch length and the exception will be raised. The new argument can take other values like int or float as well.
